CRUSTACEA : Decapoda : InachidaeCRABS, SHRIMPS AND LOBSTERS

Inachus leptochirus Leach, 1817


Description: A small spider crab with a triangular carapace up to 30 mm in length. The colour of the carapace is usually grey to yellowish brown, with the pincers and legs a lighter colouration, although the colour and features are often obscured by fauna growing on the crab’s body. There is a small and narrow u-shaped rostrum between the eyes. The eyestalks are covered with long bristles, and are the legs and carapace with hook-shaped bristles (although this is often not visible due to epifauna). Males have much larger pincers than the females. All walking legs are similar in width.

Habitat: Found from the lower shore to around 160 m. Usually found on stone or shell substrate, but also occasionally reported from muddy sand and Modiolus beds.

Distribution: Recorded all around Britain and Ireland.

Similar Species: Could be confused with other Inachus spp. Inachus dorsettensis has a wide U-shaped rostrum while Inachus phalangium has a narrow v-shaped rostrum and I. leptochirus has a narrow u-shaped rostrum. I. leptochirus has walking legs of equal width, whilst the first walking legs of the other species are noticeably wider than the others.

Key Identification Features:

  • Triangular carapace, usually covered in epifauna.
  • Narrow u-shaped rostrum between the eyes.
  • All walking legs of similar width.

Distribution Map from NBN: Inachus leptochirus at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Inachus leptochirus at iNaturalist World Species Observations database.

WoRMS: Inachus leptochirus at World Register of Marine Species. Accepted name: Inachus leptochirus Leach, 1817. AphiaID: 107330.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Brachyura; Eubrachyura; Heterotremata; Majoidea; Inachidae; Inachinae; Inachus

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 Picton, B.E. & Morrow, C.C. (2024). Inachus leptochirus. Leach, 1817. [In] Encyclopedia of Marine Life of Britain and Ireland.
https://www2.habitas.org.uk/marbiop-ni/speciesaccounts.php?item=S25770. Accessed on 2025-02-10